The invention relates generally to line drivers and more specifically to an echo and distortion cancellation arrangement in line drivers.
In a line driver connected to a telephone line for transmitting signals generated by a signal source and receiving signals incoming on the transmission line, echoes and distortions caused by the line driver itself as well as by the signal source appear together with the signals to be transmitted and the signals to be received across the output terminals of the line driver.
With long transmission lines, the received signals are only fractions of the transmitted signals at the line driver output.
The object of the invention is to reduce such echoes and distortions in the receive path of the line driver.
This is attained in accordance with the invention by providing an additional driver for driving a separate load with the same voltages and currents in its signal path as the xe2x80x9cnormalxe2x80x9d line driver.
The additional driver is, thus, not affected by signals received on the telephone line since it, instead, is connected to that separate load.
Thus, the additional driver mirrors the signal to be transmitted by the xe2x80x9cnormalxe2x80x9d line driver with the same distortion and signal levels to the separate load.
By subtracting the signal on the telephone line, which includes both the large transmitted signal with its related distortion and the often small received signal, from the signal xe2x80x9ctransmittedxe2x80x9d to the separate load by the additional driver, which only includes the large transmitted signal and its related distortion, the difference will ideally be the signal received on the telephone line, reduced from the transmitted signal as well as the transmitted distortion and noise.
Since the transmitted signal has the same currents and voltages in the signal path through both the xe2x80x9cnormalxe2x80x9d line driver and the additional driver, and both the line driver and the additional driver are preferably fabricated on the same die, the difference in distortion and voltage levels of the transmitted signals will be minimized.